PROCESS FOR APPLYING A FOAMED COATING TO A MEDICAL ADHESIVE TAPE

Abstract: This invention generally relates to a process for applying a foamed coating to a web and particularly relates to a process for applying a foamed release coating to a porous, pressure sensitive adhesive medical tape backing. The disclosed process may be used, for example, to apply a thin, uniform release coating to a porous pressure sensitive tape and includes the steps of i) forming a porous tape backing having at least one surface from polymeric fibers, ii) forming a foam of a release coating, wherein the foam is prepared by mixing water, the desired coating, and a surfactant to give a foam composition that collapses immediately when the foam composition is applied to the porous tape backing, iii) applying the foam to at least one surface of the porous tape backing to give a coated tape backing, and iv) coating the tape backing with a pressure sensitive adhesive before or after the relase coating is applied. A related process to apply a foamed latex adhesive to an elastomeric tape backing is also disclosed.

Description: PROCESS FOR APPLYING A FOAMED COATING TO A MEDICAL ADHESIVE TAPE BACKGROUND This invention generally relates to a process for applying a foamed coating to a web and particularly relates to a process for applying a foamed release coating to a porous, pressure sensitive adhesive medical tape backing. Pressure sensitive adhesive tapes for medical purposes place special demands on the components used to make these tapes. In particular, the components making up the tape must be accommodated by the user, i.e., biocompatible. Furthermore, the adhesives and coatings must not be undesirably transferred to the user during use. Briefly put, when pressure sensitive tapes are adapted for medical use, stringent demands are placed on the materials and processes used to make such tapes. Pressure sensitive adhesive tapes are typically made from polymeric films, paper, woven fabrics or nonwoven tape backings coated with a pressure sensitive adhesive on one side or surface of the backing and with a release coating on the other side of the backing. The release coating allows the coated tape backing to be rolled onto itself and prevents the transfer of the adhesive on the tape from one layer of tape in the roll to an adjacent layer. A variety of release coatings have been used for this particular purpose. Until recently, typical release coatings were dissolved in a volatile organic solvent to give a mixture or solution that was then applied to one side or surface of a tape backing using a variety of methods. For example, mixtures or solutions of release coatings and volatile solvents have been applied to tape backings using rollers, dips, knife coaters or other common application apparatus. The problems caused by using mixtures or solutions of release coatings and volatile organic solvents has prompted the development of water-based release coatings. Various methods of applying water-based release coatings have been reported. For example, U.S. Patent 4,973,513 reports that a water-based release coating may be applied to a pressure sensitive adhesive tape using conventional coating processes such as wire-wound rod, reverse roll, air knife, direct and offset gravure trailing blade, print bond or spray coating. U.S. Patent 5,089,296 reports that release coatings may be foamed and then applied to paper and other substrates. In this patent, the foams are slow breaking and require an external force such a mechanical compression or vacuum to collapse. It is also reported that control of the collapse of the foam is important because the foams rapidly penetrate and impregnate surfaces after the foam has collapsed. When a release coating is applied according to the reported process, the release coating composition must not be fast wetting in order to insure that the release coating remains on the surface of the substrate. This patent indicates that fast breaking foams are not acceptable for coating processes because migration of the release coating into a tape backing would be expected. In spite of the many different ways a release coating may be applied to a pressure sensitive adhesive, there is no single process which is believed to be preferred in any specific application. Further, there is no report that a particular process would provide the superior properties required of a medical adhesive tape. Thus, those of ordinary skill in the art are confronted with a plurality of methods or processes which might be used to manufacture a medical adhesive tape but are not provided with a process which is known to provide the tape with the required superior properties. In short, a need exists for a process to apply a release coating to a medical adhesive tape which will both reliably and predictably provide a superior medical pressure sensitive adhesive tape. SUMMARY OF THE INVENTION The present invention provides a process for applying a foamed coating to a medical pressure sensitive adhesive tape. The present process may be used to apply a thin, uniform coating, such as a release coating or a low adhesion backsize, to a porous, pressure sensitive tape backing and includes the steps of i) forming a porous tape backing having a least one surface from polymeric fibers, ii) forming a foam of an aqueous emulsion to give a foamed emulsion, wherein the foamed emulsion is prepared by mixing water, an aqueous emulsion, and a surfactant to give a foam that collapses immediately when the foamed emulsion is applied to the tape backing, iii) applying the foamed emulsion to at least one surface of the tape backing to give a coated tape backing, and iv) coating the tape backing with a pressure sensitive adhesive. Suitable tape backings include both woven and nonwoven fabrics, webs containing elastomeric fibers or yarns, and laminated or composite porous backings. Depending on the particular type of pressure sensitive adhesive tape desired, the present invention also includes a process in which the pressure sensitive adhesive is applied to the tape backing before the application of the release coating. In one example of this embodiment, the process would include the steps of i) forming a porous tape backing having at least one surface from polymeric fibers, ii) coating at least one surface of the tape backing with a pressure sensitive adhesive, iii) forming a foam of a release coating to give a foamed composition, wherein the foam is prepared by mixing water, the release coating, and a surfactant to give a fast breaking foam composition that collapses immediately when the foam composition is applied to the porous tape backing, and iv) applying the foamed emulsion to one surface of the porous tape backing containing the pressure sensitive adhesive to give a coated pressure sensitive adhesive tape. Advantageously, when a release coating or low adhesion backsize are applied to a tape backing using the present process, there is no need to use any external force to break the foamed coating. It has also been found that the use of a fast breaking foam does not cause undue migration of a coating into the porous tape backing. Control of excessive migration is especially important in a medical tape because it is believed that migration of the coating may lead to inadequate attachment of the adhesive to the tape backing. If the adhesive attachment is insufficient, adhesive residue may be left on a patient. The present process therefore may be reliably performed with much simpler apparatus than previously reported which avoids critical or complicated foam application, spreading or breaking equipment, reduces the amount of release coating which must be applied to the backing, removes potential for mechanical failure, allows high tape backing throughput and ensures proper adhesive attachment to the tape backing. In addition, the present process may be used to produce pressure sensitive adhesive tapes which are capable of passing the stringent requirements associated with medical pressure sensitive adhesive tapes. In particular, the present process provides pressure sensitive adhesive tapes which may be used in a variety of medical applications. In another embodiment of the present process, a fast breaking foam of a natural rubber latex may be used to apply a thin, uniform coating of an aqueous natural rubber latex emulsion to a woven or nonwoven elastomeric backing. This process is essentially the same as the process for applying a release coating to a tape backing except that a porous elastomeric material is used as the backing. This process includes the steps of i) forming a porous, elastomeric backing having a least one surface, ii) forming a foam of an aqueous natural rubber latex emulsion to give a foamed emulsion, wherein the foamed emulsion is prepared by mixing water, natural rubber latex, and a surfactant to give a foam that collapses immediately when the foam is applied to the porous, elastomeric backing, iii) applying the foamed emulsion to both surfaces of the elastomeric backing to give a coated backing, and iv) drying the coated backing. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a tape coating process in which a fast breaking foam is applied to a tape backing. No mechanical apparatus or externally applied force is used to break the fast breaking foam. Figure 2 is a schematic representation of a tape coating process in which a slow breaking foam is applied to a tape backing and the applied foam is then mechanically broken on the surface of the backing. Figure 3 is a schematic representation of a tape coating process which applies a foamed natural rubber latex to an elastomeric backing. Figure 4 is a schematic representation of a tape coating process which applies a foamed release coating and a transfer adhesive to a tape (with removal of the liner after application of the transfer adhesive). DETAILED DESCRIPTION The process of this invention is readily adapted to typical processes used to make pressure sensitive adhesive tape. Some typical processes currently used to make pressure sensitive adhesive tapes include forming a web from a fibrous material and then adhering the fibers of the web together with a wet binder. The wet web is then dried at elevated temperatures to give a tape backing. A release agent is then applied to one surface of the tape backing and the coated backing is again dried. Finally, a pressure sensitive adhesive is applied to the surface of the tape backing which is not coated with the release agent, the tape backing is again dried and then the tape is wound into rolls. Apparatus to perform coating processes are illustrated in Figs. 1-4. Figure 1 is a schematic illustration of a tape coating process of the present invention in which a fast breaking foam of a low adhesion backsize emulsion is applied to a binder wet web tape backing. A backing 10 is led from a nonwoven maker (not shown) and passes between binder application rollers 12 and 14. Binder is applied from station 13 by doctor blade 11. The backing proceeds to a foam coating station at which a fast breaking foam 16 is applied from a foam die 18. The applied foam coating 16 is dried by oven 20. Figure 2 is a schematic illustration of a known tape coating process in which a slow breaking foam of a low adhesion backsize emulsion is applied to a thermal bonded binder wet tape backing and the applied foam is then mechanically broken on the surface of the backing. A backing 22 is led from a nonwoven maker (not shown) between binder application rollers 24 and 26. Binder is applied from station 25 by doctor blade 27. The backing proceeds to a coating station at which a slow breaking foam 28 is applied from a foam die 29 and the foam is broken as the coated backing passes under a plastic knife edge spreader 21. The applied coating 28 is dried by oven 20. Figure 3 is a schematic illustration of a tape coating process of the present invention in which a foamed natural rubber latex is applied to an elastomeric backing. Elastic yarns 36 are led from supply spools 34 through combs 35 and then between pressure rollers 38 and 40 so that the elastic yarns will be placed between two layers of nonwoven backing 32 which are unrolled from supply rollers 30 A and 30B. The layered construction is carried between roller 42, which applies a noncohesive elastomer binder from coater 44, and roller 46 to foam dies 48 and 50 which apply natural rubber latex foam and then through oven 52 to dry the composite web 53. The dried web 53 is then directed through a pair of nip rollers 54 and 56 and through an oven 58 which is sufficiently hot to effect shirring and heat-setting as described in U.S. Patent 3,575,782 (Hansen) and then through a pair of nip rollers 60 and 62 and wound into a roll with the aid of a winder roller 72. Figure 4 is a schematic illustration of a tape coating process in which the process illustrated in Figure 3 applies a foamed low adhesion backsize emulsion from foam die 50 and is expanded by applying a transfer adhesive to the web 53 after it has exited oven 52, with subsequent removal of the transfer tape liner. The transfer adhesive on a liner 66 is supplied from roller 64 and the resulting laminate 67 is carried between nip rolls 54 and 56 with removal of liner 70 to roll 68 while web 59 is carried through oven 58 and wound into a roll. Nonwoven webs for use in preparation of porous tape backings are made in accordance with conventional methods known in the art, including wet laid methods, dry laid methods such as air layering and carding, and direct laid methods such as spunbonding and meltblowing. Examples of such methods are disclosed in U.S. Patent 3,121,021 (Copeland) and U.S. Patent 3,575,782 (Hansen). Conventional woven webs and other porous webs may also be used in the process of this invention. The nonwoven web is formed from synthetic or natural fibers selected according to the desired properties of the resulting web. Examples of textile fibers appropriate for use in the backing webs include polyester, polyolefin, polyamide, rayon, cotton, or the like. The nonwoven web may also incorporate reinforcing filaments, such as polyester, or shirring fibers such as LYCRA spandex yarns. The fibers are preferably coated with a water-based binder to give a suitable tape backing. Examples of such binders include latexes incorporating acrylics, styrene/butadiene rubbers, vinyl acetate/ethylenes, vinyl acetate/acrylates, polyvinyl chloride, polyvinyl alcohols, polyurethanes and vinyl acetates. Such binders are typically applied to the fibers at 25-35 weight percent solids by any suitable coating method, including wire-wound rod, reverse roll, air knife, direct and offset gravure, trailing blade, print bond and spray coating methods. The binder is applied in amounts sufficient to provide the desired properties to the backing, typical amounts for different types of backings would be readily apparent to the skilled artisan in the nonwoven manufacturing field. For example, more binder may be applied to produce a stronger material, which is usually stiffer, of a similar construction. After the binder has been applied, and either before the tape backing is dry or after the tape backing has been dried, a water-based release coating is applied using the process of the present invention. The water-based release coating materials include polyethylenes, fluorochemicals, acrylates, silicones, vinyl copolymers and combinations of these polymers with other polymers. Preferably, the release coating is a low adhesion backsize comprising poly(dimethyl siloxane) and acrylate polymers. Acceptable low adhesion backsizes are disclosed, for example, in U.S. Patent 4,728,571 (Clemens, et al.). Methods of foaming a release coating are also known in the art. In the practice of the present invention, a release coating is preferably mixed with more than about 0.5 weight percent of an anionic or nonionic surfactant. A preferred surfactant is an anionic surfactant such as TRITON GR-5M or a nonionic surfactant such as TRITON X-100 (both surfactants are available from Rohm and Haas Company, Philadelphia, PA). Typical blowing ratios for the foamed release coatings are from about 4 to 30. Preferred blow ratios for foaming a release coating are 20 to 30. Preferred blow ratios for foaming a natural rubber latex are 8 to 12. Suitable foams for use in the present invention may be prepared using conventional methods and apparatus. For example, a foamed release coating or a foamed natural rubber latex may be prepared in a commercially available foamer such as a LESS SUPERFOAMER foaming apparatus (Latex Equipment Sales and Surface, Palton, GA). The SUPERFOAMER apparatus is particularly convenient because it is equipped to pump the foamed material under pressure directly to a foam die. The foam die provides a back pressure and an appropriate delivery rate of the foam. After the release coating or rubber latex is foamed, the foamed material is pumped to a foam die and then applied to the tape backing by the die. The amount of material which is coated onto the tape backing is controlled by the rate the material is pumped through the die. In the present process the rate is set to deliver a thin coating at a rate of less than about 4.0 g/m 2 of a dry release coating to the tape backing (measured as difference of the dry tape backing from the dry coated tape backing). Preferably, the rate of delivery is about 0.5-1.5 g/m 2 . The rate of delivery for applying a thin coating of a dry rubber latex to a tape backing is about 5 to 7 g/m 2 per side. In addition to delivering the foam to the tape backing, the foam die also controls the uniformity of the foam applied across the width of the tape backing. A foam die which particularly applies a uniform coating from the die uses the foam emission nozzle described in U.S. Patent 4,655,056 (Zeiffer). This type of die is properly shaped to deliver a uniform flow of foam across the width of the tape backing and provides an edge-center-edge weight percent distribution of less than about plus or minus 8 weight percent. Other types of foam dies which are capable of delivering foam to a tape backing in such a controlled manner may be used in the present process. After the release coating has been applied, the coated tape backing is dried using any appropriate drying means. For example, drying means that are conventional in the nonwoven textile arts include contact drying, circulating air ovens, impingement ovens and through-air ovens. Preferably, the tape backing is dried in a circulating air oven at about 145-155°C for about one minute. The heat source is preferably located on the same side of the tape backing in the oven as the release coating, so that wicking of the release coating through the web is not encouraged by uneven drying. It is envisioned that on production scale equipment, the wet release coated tape backing will be conveyed to the drying oven about 0.5-10 seconds after application of the release coating. At this point, the coated tape backing may be wound in a roll for transportation for later application of an adhesive, or it may be conveyed directly to an adhesive coater, followed by slitting into individual tape rolls. Alternatively, adhesive may be applied as a transfer adhesive from a liner. The pressure sensitive adhesive that is applied to the nonwoven tape backing may be solvent-based, water based, or a hot melt adhesive. Suitable adhesives such as phenolic cured rubber based adhesives are disclosed in U.S. Patent 2,708,192 (Joesting et al.). Both water-based and solvent-based adhesives are disclosed in U.S. Patent RE 24,906 (Ulrich). Hot melt adhesives are disclosed, for example, in U.S. Patent 4,833,179 (Young et al.). Surprisingly, it has been observed that there is minimal migration of the release coating into the tape backing except adjacent to the area of application. In other words, the release coating does not diffuse through the tape backing as would be expected of a fast breaking foam applied to a porous material. Minimal migration of the release coating into the tape backing is demonstrated by measurement of adhesive residue left on a surface after the tape has been applied. A suitable residue test is described in U.S. Patent 4,693,776 (Krampe et al.). In another embodiment of the present invention, a foamed natural rubber latex is applied to an elastomeric tape backing. Processes to prepare a porous, elastomeric backing are known in the art. For example, an elastomeric self-adhering bandage is described in U.S. Patents 3,575,782 (Hansen) and 4,984,584 (Hansen et al.). Briefly, elastic yarns are bonded between two layers of a nonwoven web with a natural rubber latex to provide a backing having good compression characteristics and cohesiveness or the ability to self adhere. The following examples are provided to further illustrate the practice of the present invention. The examples should not be construed to limit the invention which is defined in the appended claims. EXAMPLES Example 1 Processes Using Mechanical Breaking of an Applied Foam Using an apparatus illustrated schematically in Figure 2, 30 yards (27.4 m) by 20 inches (50.8 cm) in width and 3.5 mils (0.0889 cm) in thickness of 80:20 polyethylene terephthalate: a nonwoven web was prepared from a blend of 80 parts T-121 staple polyester fiber, 1.2 denier 38 mm polyethylene terephthalate available from Hoechst Celanese Corp., Charlotte, NC and 20 parts of 2 denier 38 mm type K-54 MELTY type binder fiber (a core-sheath fiber containing an oriented polyester core and a meltable polyester sheath also available from Hoechst Celanese Corp., Charlotte, NC) were processed in a Hergeth Random-Card machine (available from Hergeth Hollingsworth GMBH, Dulman, West Germany) utilizing conventional nonwoven web formation techniques to produce an approximately 35 g/m 2 basis weight nonwoven web. The nonwoven web was embossed using a heated calender and then was wet with 25 wt. % solids acrylic/vinyl acetate copolymer latex binder (available from National Starch Company, Bridgewater, NJ as 78-6283) to give nonwoven tape backing. The wet tape backing was treated with a foamed release agent. The foam was made by a LESS foaming apparatus (available from Latex Equipment Sales and Service, Palton, GA, as SUPERFOAMER model) from a 2 wt. % aqueous solution of water-based low adhesion vinyl silicone copolymer backsize (prepared as described in U.S. Patent 5,032,460 (Kantner et al.)) of 20/50/10/30 methyl acrylate/methyl methacrylate/methacrylic acid/mercapto dimethyl siloxane. The foam was applied using a knife edge type system of a straight edge of hard plastic sheeting 100 mils (2.54 mm) thick by 4 inches (10.2 cm) wide by 36 inches (91.4 cm) long. The foam covered backing was carried at 15 feet per minute (4.57 m/min) into and through an oven at 325-350 °F (163-177°C) and the dried backing web was wound onto a 3 inch (7.6 cm) core. The coated backing was then coated full width at 6.5 grains/24 in 2 (27 g/m 2 ) using a semi- wet lamination process generally described in U.S. Patent 3,121,021 (Copeland) with a water based 40 to 44 wt. % 95:5 isooctyl acrylate: acrylic acid polymer adhesive prepared as described in U.S. Patent Re 24,905 (Ulrich) to provide a medical adhesive tape. The tape was then slit into one inch (2.54 cm) wide by 10 yards (9.1 m) long rolls. The rolls were found to unroll readily after aging for 2 days at 120°F (49°C) at 90% relative humidity. However, the adhesive attachment to the coated backing was not adequate because an adhesive residue was left on the skin when the medical tape was used. Specifically, the amount of adhesive residue was more than about two times the adhesive residue when compared to a similar tape prepared by spraying the low adhesion backsize onto the backing as generally described in U.S. Patent 4,973,513 (Riedel et al.). The decrease in adhesive attachment to the backing is a result of low adhesion backsize penetration into the backing when the foam was mechanically broken on the backing surfacing using the plastic knife edge. Another tape backing was prepared from standard viscose processed rayon staple fibers (1.5 denier, 40 mm length, available from Courtaulds North America, Inc., New York, N.Y.) in a Hergeth Random-Card machine to produce an approximately 22 g/m 2 basis weight nonwoven backing. Using the apparatus of Figure 2 about 50 yards (45.7 m) of the rayon backing was either wet treated with various binders at 28 v -. % aqueous solids loading or treated with the binders at 28 wt. % aqueous solids and dried, and then was froth coated according to the procedure described above with a 2 wt. % solution of the low adhesion backsize containing a surfactant added (0.5 wt. % TRITON GR-5M, available from Rohm and Haas Company, Philadelphia, PA). The line speed was 15 feet/minute (4.57 m/min) and the oven temperature was 340 °F (171 °C). Spreading was done by an idler arm or a wipe blade. Specific processing conditions are listed in Table 1 below. After the listed tapes were coated and dried, they were aged for 2 days at 120°F (49°C) at 90% relative humidity. Roll unwind of the aged tapes was determined according to ASTM D-1000. The roll unwind was 450 g/2.54 cm and found to be unsatisfactory. In addition, the adhesive attachment was determined for the listed tapes and it was found that the adhesive residue was above acceptable levels for a medical adhesive tape. TABLE 1 Latex Parameters Foam Generator LAB Solution LAB Coating Sample Air Air Method Spreader Pump Blender Flow Inlet Back P Solids GR-5M Binder pH (rpm) (rpm) (slm) (psi) (psi) (%) (%) 1 B-15H 1 6.0 none Idler 2 B-15H 6.0 15 200 2.9 40 6 2 0.5 wet on dry Idler 3 B-15H 6.0 15 250 2.9 40 6 2 0.5 wet on wet Idler 4 B-15H 6.0 15 200 2.2 40 6 2 0.5 wet on wet Idler 5 NS 2 6.0 none Idler 6 NS 6.0 15 230 2.2 40 6 2 0.5 wet on wet Idler 7 NS 6.0 15 230 2.2 40 6 2 0.5 wet on dry Idler 8 NS 6.0 15 230 3 40 6 2 0.5 wet on dry Idler 9 4402 3 8.5 none Idler 10 4402 8.5 15 230 2.2 40 6 2 0.5 wet on wet Idler 11 4402 8.5 15 230 1.6 40 6 2 0.5 wet on wet Idler 12 4402 8.5 15 230 2.2 40 6 2 0.5 wet on dry Idler 13 4402 8.5 15 230 3 40 6 2 0.5 wet on wet Doctor LAB-low adhesion backsize 1 B15H is a binder available from Rohm and Haas Company, Philadelphia, PA 2 NS is a binder available from National Starch used in Example 1 3 4402 is styrene-butadiene rubber binder available from Unical Corp., Charlotte, NC as UC 4402 Example 2 Foam Release Coating Process Medical adhesive tapes were prepared according to the process generally described in Example 1 above except that no mechanical means were used to break or spread the foam after it was applied to a tape backing as illustrated schematically in Figure 1. More specifically, a rayon backing was prepared from 1.5 denier and 1-9/16 inch (3.97 cm) long fibers using the process described in Example 1. The web had a basis weight of 20 g/m 2 and was about 12 to 14 inches (30.5 to 35.6 cm) wide and was trimmed to 12 inches (30.5 cm) wide. It was coated at a speed of about 30 to 35 feet/minute (9.1 to 10.7 m/min) with a variety of binders as shown in Table 2 to a ratio of about 1 g of binder to 1 g of web fiber using suspensions of 26 wt. % binder solids at pH 7.5 to 8.5. After the binder was coated on, the low adhesion backsize used in Example 1 was coated as a foam using the foamer described in Example 1 and a Gaston County 0.25 inch (0.635 cm) oriface parabolic die. The low adhesion backsize included 1.25 wt. % GR-5M surfactant and was applied at a 22: 1 blow ratio. Specific processing conditions are listed in Table 2 below. After the listed tapes were coated and dried, they were aged for 2 days at 120°F (49 °C) at 90% relative humidity. Roll unwind of the aged tapes was determined according to ASTM D-1000. The roll unwind was less than 350 g/2.54 cm. In addition, the adhesive attachment was determined for the listed tapes and it was found that the adhesive residue as determined according to the procedure listed in U.S. Patent 4,693,776 (Krampe et al.) was below a value of 2.5. These data indicate that the medical adhesive tape prepared according the process listed in the present example are acceptable for its intended use. The backings listed in Table 2 which are odd-numbered were coated with a pressure sensitive adhesive using the process described in U.S. Patent 3,121,021 (Copeland) before a low adhesion backsize was applied to the backing using the present process. TABLE 2 Sample Binder LAB Primer Yardage 1 4402 - - 50 2 4402 X - 100 3 V-43 - - 50 4 V-43 X - 100 5 6283 - - 50 6 6283 X - 100 7 4260 - - 50 8 4260 X - 100 9 HP-2931 - - 50 10 HP-2931 X - 100 11 2833 - - 50 12 2833 X - 100 13 1715 - - 50 14 1715 X - 100 15 1845 - - 50 16 1845 X - 100 17 B15 - - 50 18 B15 X - 150 19 B15 - X 50 20 Backing #18 Primed side not coated X 50 LAB: low adhesion backsize Binders: 4402 Rohm and Hass SBR 4402 V-43: B.F. Goodrich 6283: National Starch 78-6283 4260: National Starch 25-4260 HP-2931: Rohm and Haas 2833: National Starch 25-2833 1715: Rohm and Haas 1845: Rohm and Haas B15: Rohm and Haas Primer: Mica G 1147 Mica Corp. at 1 wt. % solids with 0.25 wt. % GR-5M surfactant Example 3 Elastomeric Tape Backings Treated with Foamed Compositions Using an apparatus shown diagrammatically in Figure 3, a web of 12 g/m 2 thermally bonded polyethylene terephthalate fibers of web width 16 in (40.64 cm) was prepared according to the method described in Example 1 above. A noncohesive elastomer, H stretch V-43 (available from B.F. Goodrich Company, Akron, OH) was applied to two layers of the backing sandwiching a spandex elastomeric yarn to give an elastomeric tape backing as shown in Figure 3. Cohesive elastomer natural rubber latex (available from Goodyear Rubber Plantations Company, Akron, OH) was applied as a foam to both sides of the wet elastomeric tape backing at a blow ratio of 10: 1 and dried. The coated tape backing was subsequently slit using a conventional slitting apparatus into self wound rolls. The product exhibited a light cohesion to itself after foam coating of the natural rubber latex. A similar elastomeric adhesive tape was also prepared according to the following procedure. A coating of a low adhesion backsize was applied to one side of the noncohesive polyethylene terephthalate elastomeric tape backing described above using the process of the present invention from the LESS foaming apparatus of Example 1. The low adhesion backsize used was that used in Example 1 which had been foamed at a blender speed of 153 rpm, pump speed 15 rpm, air flow setting 20, air inlet setting 40 psi and back pressure 7 psi at a blow ratio of 22:1. The release coating process was carried out at 12 ft/min (3.66 m/min) line speed, the low adhesion backsize was applied at 2.0 g/m 2 at an application rate of about 140 g/min of low adhesion backsize emulsion (2% solids in water). Then, an acrylic acid-isooctyl acrylate (4:96 molar ratio) copolymeric transfer adhesive (as described in U.S. Patent RE 24,906) coated at 60 g/m 2 on a differential release liner (liner 2-80 BKG 157/99 AM available from Daubert Coated Products, Dixon, IL) was dry laminated from the coated liner onto the uncoated side of the elastomeric backing using conventional procedures. The resulting elastomeric adhesive tape had no cohesion to the nonfoam coated web. The rolls were tested for roll unwind according to ASTM D-1000 and found to have acceptable unwind of less than 350 g/2.54 cm. The rolls were also tested for adhesive anchorage according to residue left as described above and found to be satisfactory. Example 4 Cloth Backing Treated with Foamed Low Adhesion Backsize An acetate cloth fabric pressure sensitive adhesive tape was prepared according to the following procedure. A 25 m in length by 20 cm in width of the acetate fabric (style 180 x 48 plain weave available from Milliken & Company, LaGrange, Georgia) was coated on one side with an acrylic acid-isooctyl acrylate (4:96 molar ratio) copolymer adhesive in ethyl acetate solvent prepared as described in U.S. Patent RE 24906 (Ulrich) at a rate of 60 g/m 2 and dried in an air circulating oven. Before entering the final oven drying stages a coating of low adhesion backsize was applied to the non-adhesive coated side of this backing using the process of the present invention from the LESS foaming apparatus of Example 1. The low adhesion backsize used was the vinyl silicone copolymer that was used in Example 1 which had been foamed at a blender speed of 153 rpm, pump speed of 15 rpm, air flow setting of 20, air flow setting of 40 psi and a back pressure of 7 psi and a blow ratio of 22:1. The coating process was carried out at 12 ft/min (3.66 meters) line speed, the low adhesion backsize was applied at a rate of 2.1 g/m 2 from about 140 g/min of low adhesion backsize emulsion (2% solids in water). The resulting adhesive tape rolls were tested for roll unwind according to ASTM D-1000 and found to have acceptable unwind of less than 350 g/2.54 cm. The rolls were also tested for adhesive anchorage according to residue left as described above in Example 2 and found to be satisfactory, i.e., to have a value below 2.5.

Claims: CLAIMS 1. A process for applying a thin, uniform coating of a foamed composition to a surface of a porous, pressure sensitive medical tape comprising of the steps of i) forming a porous tape backing having at least one surface from polymeric fibers, ii) forming a foam of an aqueous emulsion to give a foamed emulsion, wherein the foamed emulsion is prepared by mixing water, a low adhesion backsize or release coating, and a surfactant to give a foam that collapses immediately when the foamed emulsion is applied to the tape backing, iii) applying the foamed emulsion to at least one surface of the tape backing to give a coated tape backing, and iv) coating the tape backing with a pressure sensitive adhesive. 2. The process of claim 1 wherein the foamed emulsion is applied to the tape backing using a foam nozzle under pressure. 3. The process of claim 1 wherein the low adhesion backsize is applied to the tape backing at a rate of about less than 4 g/m 2 when dry. 4. A process for applying a thin, uniform coating of a foamed composition to a surface of a porous, pressure sensitive medical tape comprising of the steps of i) forming a porous tape backing having at least one surface from polymeric fibers, ii) coating at least one surface of the tape backing with a pressure sensitive adhesive, iii) forming a foam of an aqueous emulsion to give a foamed emulsion, wherein the foam composition is prepared by mixing water, a low adhesion backsize or release coating, and a surfactant to give a foam composition that collapses immediately when the foam composition is applied to the porous tape backing, and iv) applying the foamed emulsion to one surface of the porous tape backing to give a coated pressure sensitive adhesive tape. 5. A process for applying a thin, uniform coating of an aqueous latex emulsion to a woven elastomeric backing comprising the steps of i) forming an elastomeric backing having at least one surface, ii) forming a foam of the aqueous latex emulsion to give a foamed latex emulsion, wherein the foamed latex emulsion is prepared by mixing water, latex, and a surfactant to give a foam that collapses immediately when the foamed latex emulsion is applied to the woven elastomeric backing, iii) applying the foamed latex emulsion to both sides of the elastomeric backing to give a coated backing, and iv) drying the coated backing. 6. The process of claim 5 wherein the latex is applied to the elastomeric backing at a rate of less than about 10 g/m 2 .

Inventors: CRAN LAUREN E, RIEDEL JOHN E, CRAN, LAUREN, E., RIEDEL, JOHN, E.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1994
Main classification: A61F13
IPC codes: A61F13, C09J7, D06M23, D06N3